Conventionally, a patent document 1 discloses a common driving force distribution device. The driving force distribution device disclosed in this document is a transfer of a four wheel drive vehicle, which includes a planetary gearset, and sets driving force distribution (torque distribution) between main and auxiliary driving wheels, wherein a torque from a transmission is inputted into a carrier of the planetary gearset, and the torque is split and outputted from the carrier through a sun gear and a ring gear to the main driving wheels and the auxiliary driving wheels.    Patent Document 1: JP 2005-337442 A